High speed impact printer

ABSTRACT

A high speed mechanical impact printer using a continuously rotating print wheel. Paper label stock is contained on a supply reel and fed through a print station comprising the print wheel and a print hammer by a motor and roller means positioned beyond the print station. Substantially constant tension is maintained between the supply reel and the print station by a spring assisted tension means operating in conjunction with the supply reel. The print wheel is secured to a belt-driven, printer drive member through a compressible plastic ring. In printing, a hammer impacts the label stock and an ink ribbon against the rotating print wheel under logic control. After printing, the stock proceeds through a mechanical means which permits the operator to conveniently strip the most recently printed label from the stock backing so that he may attach it to a commercial item or the like.

United States Patent Brooks Feb. 18, 1975 1 HIGH SPEED IMPACT PRINTER [57] ABSTRACT [75] Inventor: Robert J. Brooks, Bellevue, Wash.

[ 1 Assigneei Interface Mechanisms Inc-r A high speed mechanical impact printer using a con- Mountlake Terrace Wash" tinuously rotating print wheel. Paper label stock is 22 Filed; O 3, 1973 contained on a supply reel and fed through a print sta- Appl. No.: 403,277

Primary ExaminerEdward J. McCarthy Attorney, Agent, or Firm-Cristensen, OConnor, Garrison & Havelka tion comprising the print wheel and a print hammer by a motor and roller means positioned beyond the print station. Substantially constant tension is maintained between the supply reel and the print station by a spring assisted tension means operating in conjunction with the supply reel. The print wheel is secured to a belt-driven, printer drive member through a compressible plastic ring. In printing, a hammer impacts the label stock and an ink ribbon against the rotating print wheel under logic control. After printing, the stock proceeds through a mechanical means which permits the operator to conveniently stripthe most recently printed label from the stock backing so that he may attach it to a commercial item or the like.

8 Claims, 11 Drawing Figures PATENTED 3 866 851 SHEET E U F 3 1 HIGH SPEED IMPACT PRINTER BACKGROUND OF THE INVENTION This invention relates generally to printing devices, and more specifically, to the art of high speed mechanical impact printers.

Mechanical impact printers are generally well-known in the art, although frequently such printers must be specially adapted for particular applications. The printing of bar codes, such as that disclosed in U.S. Pat. No. 3,700,858 to Murthy, for purposes of high speed item identification, requires high resolution, accurately spaced, printing. The individual characters must be clear and precise, and the separation between characters accurate and uniform. If such high resolution, uniform printing is not maintained, errors in reading the bar code will increase, to the detriment of the identification system using the code.

Furthermore, in the printing of label stock, the operator of prior art printers must peel off the individual labels manually from the stock backing after they are printed in order to affix them to the commercial item; e.g., carton, which is to be identified. This manual stripping of the labels from the stock backing is often impractical as it can only be accomplished some distance away from the rotating printing element.

Thus, there is a current need in particular printing applications for an impact printer, otherwise utilizing conventional impact printing principles, which is capable of printing high resolution, accurately spaced, characters for particular code printing applications, and in the case of label stock, for a means which presents the labels to the operator after printing in a condition such that they may be readily stripped and affixed to the item to be identified. In accordance with the above, it is a general object of the present invention to provide a mechanical impact printer which overcomes the disadvantages of the prior art.

It is another object of the present invention to provide an impact printer wherein the printing stock supply reel has a tensioning means in conjunction therewith for maintaining a substantially constant tension on the printing stock.

It is a further object of the present invention to provide an impact printer in which the time for actuation of the print hammer is substantially decreased.

It is yet another object of the present invention to provide a mechanical impact printer having a print wheel which is rotated by means ofa compressible ring connection between the driving means and the print wheel.

It is a still further object of the present invention to provide a mechanical impact printer wherein labels may be individually stripped immediately after printing is accomplished.

SUMMARY OF THE INVENTION According, a tensioning apparatus is provided which includes a rotatable spindle for positioning a supply reel on which printing stock is conventionally wound. A reel arm assembly is rotatably secured at one end in the vicinity of the spindle, and a guide is provided at the other end of the reel arm assembly, with the printing stock being passed around the guide and to the printing station from the supply reel. A braking means acts on the spindle of the supply reel and is controlled by the relative position of the reel arm assembly, which reel arm assembly tends to remain in a given position because of the action of a spring means. The pressure of the print stock against the guide will increase and decrease according to the tension exerted on the print stock. This pressure will result in rotation of the reel arm assembly, which in turn acts on the braking means, increasing or decreasing the pressure on the spindle.

DESCRIPTION OF THE DRAWINGS FIG. 3 isapl an view of the label stripper mechanism of the present invention.

FIG. 4 is an isometric view of the tensioning means associated with the stock supply reel of the present invention.

FIG. 5 is a partial section elevation view of the print hammer actuator mechanism of the present invention.

FIG. 6 is a section view of the print wheel of the present invention.

FIG. 7 is a simplified representation of the print hammer actuator mechanism of the present invention.

FIG. 8 is a graph of the motion of the print hammer against time during actuation.

FIG.9 is a graph of the current through the coil of the print hammer actuator mechanism of FIG. 7 against time during actuator.

FIG. 10 is a top plan view of the compressible pad of the present invention.

FIG. 10a is a section view of the compressible pad, taken along lines 10a-l0a in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an isometric view of the impact printer of the present invention is shown. As in prior art printers, input power is supplied via a standard volt line (not shown) to a power supply module 12, which in turn provides power for the printer, including the logic control circuit 14. Signals from peripheral equipment can be connected into the printer through connector 16 to the motor drive circuit 18, and the logic control circuit 14. These two circuits 18 and 14 control, in conventional fashion, the operation of the printer. Printing stock 19 is typically stored on a supply reel 20, and is directed around arm 22, through stock sensor 24, through a print station, comprised of print hammer assembly 26 and a cylindrical print wheel 28, through a label stripper 30, and then through a stock stepper assembly 32, which typically contains a motor drive and a pair of rollers, for placing the printing stock under tension.

The ink ribbon 34 is typically stored on a supply reel 36, first positioned partially around guide pin 38, then directed between the printing stock 19 and the circumferential surface of the print wheel 28 before going through a powered ribbon drive assembly 40, and finally wound up on a ribbon take-up reel 42 which is driven by motor 44. The print wheel 28 is continuously rotated in operation by means of drive motor 46 acting through a drive wheel 54 and belt 48.

In operation, print wheel 28, having a set of raised print characters arranged around its circumferential surface, continuously rotates by means of drive motor 46, and the ribbon 34 and printing stock 19 are pulled past the print station comprising print hammer assembly 26 and print wheel 28 by means of their respective take-up motors. The logic control board 14 issues signals commands to the print hammer assembly 26, which signal commands actuate the print hammer to impact the printing stock 19 and the ribbon 34 sufficiently against the circumferential surface of the print wheel 28 that a single raised character is imprinted on the stock 19. A system for synchronizing the operation of the rotating print wheel and the hammer assembly is disclosed in copending application Serial No. l 10,517, filed January 28, I971, entitled High Speed Printer and is assigned to the same assignee as the present invention. Briefly, such a synchronization system utilizes a cylindrical code wheel, attached to the print wheel and rotating therewith, which code wheel has a plurality of coded holes patterns, one for each print character, located therein. Photoelectric means is used to detect the hole patterns, which data is in turn applied to a circuit which compares the code data with signals representing the desired character selected at a keyboard or similar device. When there is a coincidence, the print hammer is actuated, resulting in the desired character being printed.

Referring now to FIG. 6, a cross section view of the print wheel assembly of the present invention is shown. The print wheel assembly consists generally of: a housing 52, which is attached to the deck of the printer; a drive assembly comprising drive wheel 54, bearing 56 and drive shaft 58; print wheel 60; securing knob 62; and a compressible plastic ring pad 64. In operation, motor 46 (FIG. 1) rotates drive wheel 54 by means of the belt 48 (FIG. 1) connecting the motor 46 and the drive wheeel 54. Shaft 58 does not rotate with the drive wheel 54, but is anchored into the housing 54 by end bolt 57.

The print wheel 60 is secured to the rotating drive wheel 54 by means of the compressible ring pad 64, which is positioned between the drive wheel 54 and print wheel 60. The print wheel 60 is forced toward the drive wheel, compressing ring pad 64, by means of screw-adjusted securing knob 62, which is turned into the drive shaft 58. Thus, the only contact between drive wheel 54 and the print wheel 60 is through the compressible polyurethane ring pad 64, shown in position in FIG. 6, and in more detail in FIGS. and 10a. The compressible pad 64 is in the shape of a ring having outer and inner boundary surfaces 65 and 67, respectively. A trough 68, formed in the ring pad 64 enables the ring pad to be fitted snugly over a mating ring 69 in drive wheel 54. Trough 68 substantially follows the shape of the outer and inner boundary surfaces 65 and 67, resulting in a compressible ring pad having two concentric edge members 64a and 64b extending perpendicularly from a cross member 64c connecting edge member 640 and 64b and one end thereof. Extending away from surface 640' of connecting member 640 are a plurality of integral compressible hemispheres 7070, which are of the same compressible polyurethane material as the remainder of the compressible ring pad.

Print wheel 60 rests on the plurality of compressible hemispheres -70, and these hemispheres are compressed-by the action of tightening securing knob 62 into shaft 58. The friction fit between the print wheel 60, the compressible ring pad 64 and the ring portion 69 of drive wheel 54 is sufficient to rotate print wheel 60 by rotating drive wheel 54 by means of motor 46 and belt 48, without slippage between them. A bearing 66 is positioned between the print wheel 60 and shaft 58 to provide rotational freedom of movement. The friction drive of print wheel 60 accomplished by compressible ring pad 64 eliminates the need for high tolerance machining and keying to mate a print wheel with a drive wheel, as is done in the prior art. The friction drive also significantly reduces the potential for printing inaccuracies due to wear or poor machining of the print wheel 60 or the drive wheel 54. Furthermore, such an arrangement allows for the print wheel to be easily removed for cleaning or exchange, as desired, without the necessity of time-consuming realignment of the printing wheel assembly.

The print station, as mentioned above, comprises print wheel assembly 28. and the print hammer assembly 26 (FIG. 1) which is under the control of control logic circuit 14. Referring to FIG. 5, the print hammer assembly 71 is shown in a partial section view. When the hammer 71a is to be actuated toward print wheel 72, a signal is applied from control logic 14 (not shown) to an electromagnet (not shown) within the assembly. When the electromagnet is energized by current flowing through its coil (not shown) lever arm 74 which is secured to the hammer assembly 71 by flexible member 76 at one end thereof, is drawn into contact with a portion 78 of the assembly electromagnet (otherwise not shown). As lever arm 74 moves toward the magnet portion 78, hammer arm 80 moves in the direction of the arrow toward the circumferentialsurface 73 of print wheel 72. At the other end 83 of hammer arm 80 is connected hammer 710. When lever arm 74 is actuated, hammer 71a moves in the direction of the arrow toward circumferential surface 73 of print wheel 72 to such an extent as to impact the printing stock (not shown) and ink ribbon (not shown) positioned between the print wheel 72 and the print hammer 71 against a particular character 72a on circumferential surface 73.

When the current is discontinued through the electromagnet, lever arm 74 springs back away from engagement with magnet portion 78 by means of flexible member 76. The force of this spring-back is absorbed by spring loaded stop 84, and any oscillations of ham mer arm 80 are quickly damped. Such a print hammer assembly is commonly referred toas a cantilever beam assembly.

A principal disadvantage to such print hammer assemblies has been the time heretofore required to actuate and retrieve the print hammer mechanism. The response time of the mechanism is dependent on the rate of increase of current of di/dt, in the electromagnet coil. The greater the rate of increase in current over time, the faster the hammer will actuate. Heretofore, however, coil di/dt has been limited because high di/dt values have been obtained only by using actuator circuits which produce a high value of coil current for much of the hammer travel time, which results in undesirable coil heating and drive transistor strain, ultimately resulting in failure of both elements.

To prevent high heat loss and coil failure, while significantly increasing coil di/dt so as to provide faster actuation of the print hammer, the actuator circuit of the present invention has been developed. Referring to FIG. 7, a significantly higher actuating voltage V than is provided by the prior art (100 volts as opposed to approximately 25 volts) is connected through a transistor 90 and an RC circuit comprising capacitor 92 and resistor 94 to the electromagnet coil 96. Transistor 90 is controlled by a signal from control logic circuit 14 (not shown). In operation, when transistor 90 is turned on by the logic control signal, current flows primarily through capacitor 92 and coil 96. A diagram of coil current v. time is shown in FIG. 9. As the charge on capacitor 92 approaches actuating voltage V,,, the current decreases to a value dependent on resistor 94, thus limiting the energy dissipated in coil 96 to a tolerable level and easing the load on transistor 90. Because of the high initial rate of current increase, however, the hammer 97 begins to move substantially sooner than previously, and actuation time is'reduced. At 1.2 milliseconds from the start of current flow, hammer 97 impacts the paper stock and ribbon against the desired character 99. A graph of distance v. time for the travel of the print hammer is shown in FIG. 8.

Referring again to FIG. 1, printing stock 19 is directed through a print station comprising hammer assembly 26 and print wheel 28 by means of a supply reel 20, and a label stepper 32, which exerts a pulling force on stock 19. However, in certain applications, such as label printing, where the movement of the printing stock is not uniform, slack will tent to occur in the printing stock between the supply reel and the print station. Any such slack is ordinarily unsatisfactory, as it results in either distortion of the printed characters or variations in the character separation or both. The printed code is thus more difficult to accurately read and subject to an increased number of reading errors. To overcome this tendency, a tensioning means is provided by the present invention in conjunction with the supply reel 20, as shown in FIG. 4. A printing stock supply reel 100 is positioned conventionally on a reel spindle 102. In operation, stepper 32 exerts a pulling force on stock 19, and hence pressure on roller guide 104, which roller guide is rotatably mounted on one end 105 of guide arm 106. The other end 107 of guide arm 106 is fixedly connected to a rotating arm assembly 108, which comprises a cylinder 110 fixedly mounted on plate 112, which arm assembly rotates with the rotation of guide arm 106 about a fixed central shaft 114 against the tension of spring 116, one end of which is secured to a fixed peg 118, and the other end to a peg 120 on the rotating arm assembly 108. As the force on stock 101 increases in the direction of the arrow, thus forcing guide arm 106 to move counterclockwise about central shaft 1 14, the rotating arm assembly 108 also rotates counterclockwise, forcing the free end 122 of pivot arm 124 toward the periphery of supply reel 100 against the tension of spring 127. This movement of pivot arm 124 reduces the braking force of tension arm 126, which is secured to pivot arm 124, against supply reel spindle ring 128, allowing spindle 102 to rotate more freely, and thus feed printing stock 101 faster. Roller guide 104 and guide arm 106 will eventually reach an equilibrium angular position when a constant force is exerted on stock 101. However, if the force on stock 101 varies, as in label printing, the angular position of guide 104 and guide arm 106, and hence, the remainder of the system will attempt to track the force, searching" for an equilibrium position.

For instance, if the force on roller guide 104 is suddenly reduced, as would occur with the return of the stripper to its original position, the tension exerted by spring 116 will tend to rotate the arm assembly 108 in the clockwise direction, and along with it guide arm 106 and roller guide 104 until a system equilibrium is reached. Equilibrium is eventually achieved because the clockwise rotation of arm assembly 108 will allow pivot arm 124 to move in the direction of the spindle 102, under the tension of spring 127. This will increase the braking force on spindle ring 128 exerted by tension arm 126, and the supply reel will thus be increasingly braked. Such a responsive tensioning device tends to maintain that portion of printing stock 101 located between the supply reel and the print station in substantially constant tension, thus increasing printing resolution and accuracy, and hence, reducing code reading errors.

Following the print station is located a label stripper 30, shown generally in FIG. 1 and in more detail in FIGS. 2 and 3. In operation, the label stock (when used) is passed between guide elements 130 and 132, connected by support member 133. The entire stripper 30 is rotatable about axis l34--134 with respect to the deck of the printer, so that it may be conveniently taken out of operation. Guide elements 130 and 132, as well as support element 133 are rotatable about axis 135-135. By rotating the stripper about axis 135-135 in a clockwise manner from its original position by convenient means of rotation knob 142, peg 130 guides the label stock through a substantially U- shaped path before it comes to the label stepper 32. Al-

though the stock backing follows such a path, the labelsthemselves do not, and separate from the backing when the backing begins to bend to follow the U-shaped path. By thus rotating label stripper knob 142 in such a fashion, the operator is able to strip a label in close proximity to the print mechanism, and then conveniently place them, if desired, on appropriate cartons or other commercial items. Located within rotation knob 142 is a spring 140, which is secured at one end thereof such that the knob, and hence, guide pins 130, 132 are rotated against the tension of the spring. When the knob 142 is released, the action of spring 138 returns the stripper elements to their rest position of FIG. 1. Bendable stop 141 provided to lock the stripper in operating position, if desired. A spring 138 is positioned so as to place the stripper 30 and element 139 in tension along shaft 139a.

Thus, a mechanical high speed impact printer has been disclosed which utilizes a generally conventional configuration but which has several novel features to increase printing resolution, printing accuracy, and operational convenience in the printing of bar codes on labels or other printing stock.

Although an exemplary embodiment of the invention has been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow.

What is claimed is:

1. A tensioning apparatus used in conjunction with a printing stock supply reel in a high speed impact printer, comprising in combination:

rotatable spindle means for receiving said printing stock supply reel; 3 reel arm assembly rotatably mounted at one end thereof in the vicinity of said spindle means;

spring means connected to said reel arm assembly for biasing said reel arm assembly into a first angular position;

roller guide means mounted on said reel arm assembly and spaced away from said one end thereof, said printing stock, as it is unwound from said supply reel and passed partially around said roller guide means, pressing against said roller guide means and forcing said reel arm assembly to rotate about said one end against the bias of said spring means; and,

braking means mounted in the vicinity of said spindle means, said braking means engageable with said spindle means such that as said reel arm assembly rotates relatively away from said first angular position against the bias of said spring means, pressure of said braking means against said spindle means decreases, allowing said spindle means to turn more freely, said braking means including a brake arm, rotatably mounted in the vicinity of said spindle means, and operative to engage said reel arm assembly, said braking means further including a second spring means, and a spring lever mounted on said brake arm, said second spring means biasing said brake arm such that said spring lever engages said spindle means, the rotation of said reel arm forcing said brake arm to rotate against the bias of said second spring means, thereby decreasing the pressure of said spring lever spindle means.

2. An apparatus according to claim 1 wherein said roller guide is a cylindrical section, rotatably secured to said other end of said elongated reel arm assembly.

3. An apparatus according toclaim 2 wherein said reel arm assembly includes a plate member located at said one end of said reel arm assembly and rotating therewith, said first spring member being secured to said plate member, said plate member further mating with said brake arm, and being shaped such that a rotation of said reel arm assembly under stock pressure forces said brake arm to rotate in response thereto through the rotation of said plate member.

4. An apparatus according to claim 3 wherein said plate member is shaped in the vicinity of its mating with said brake arm such that when said reel arm assembly is at said rest position pressure exerted on said spindle means by said spring lever is at a maximum, and when said reel arm assembly is gradually rotated against the action of said first spring member, the accompanying rotation of said plate member gradually forces said brake arm against the action of said second spring member, gradually reducing the pressure exerted on said spindle means by said spring lever.

5. A tensioning apparatus, useful in a machine which includes a tape supply means, wherein the tape supply means includes a reel for receiving tape or the like, the machine being operative to exert a force on the tape. tending to cause the reel to rotate and the tape to unwind therefrom, the tensioning apparatus comprising: tape guide means engaging the tape as it is unwound from the reel, said tape guide means mounted to rotate about a first axis and yieldably biased into a first angular position about said first axis, said tape guide means being rotated against the bias thereon when the force is exerted on the tape by the machine; braking means yieldably biased into a stopped position engaging said tape supply means in a manner substantially preventing rotation of the reel; and,

cam means rotatable with said tape guide means and engageable with said braking means and operative upon rotation of said tape guide means relatively away from said frist angular position to displace said braking means against the bias thereon relatively away from the stopped position, permitting rotation of said reel.

6. An apparatus of claim 5, wherein said braking means is rotatable about a second axis spaced apart from said first axis.

7. An apparatus of claim 5, wherein said cam means is engageable with said braking means substantially upon initial rotation of said type guide means, said cam means being so configured as to substantially uniformly increase the displacement of said braking means relatively away from its stopped position as said cam means is rotated, thereby gradually increasing the relative freedom of rotation of said reel.

8. An apparatus of claim 5, wherein said braking means further includes means connected thereto and engaging said tape supply means in frictional engagement, the engagement of said resilient means and said tape supply means preventing rotation of the reel when said braking means is in said stopped position, the pressure of said resilient means against said tape supply means gradually decreasing as said tape guide means is rotated about said first axis under the external force, thereby permitting increasing freedom of rotation of said reel.

UNITED STATES PATENT oTTTeT @ERTWMATE @F CQRRECTWN Q PATENT NO. 2 3,866,851

DATED 3 February 18 1975 INVENTOMS) 3 Robert G Brooks It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column '7, line 33, add the words egainst said-- after the word. "lever".

Column 8, line 41, add the word -resilient--== after the 9 word. "includes" and fieaaedt Th s,

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Q Q more C. meow c. MARSHALL mm 7 Arresting Officer (ommissr'oner ofPmmls and Dademarks 

1. A tensioning apparatus used in conjunction with a printing stock supply reel in a high speed impact printer, comprising in combination: rotatable spindle means for receiving said printing stock supply reel; a reel arm assembly rotatably mounted at one end thereof in the vicinity of said spindle means; spring means connected to said reel arm assembly for biasing said reel arm assembly into a first angular position; roller guide means mounted on said reel arm assembly and spaced away from said one end thereof, said printing stock, as it is unwound from said supply reel and passed partially around said roller guide means, pressing against said roller guide means and forcing said reel arm assembly to rotate about said one end against the bias of said spring means; and, braking means mounted in the vicinity of said spindle means, said braking means engageable with said spindle means such that as said reel arm assembly rotates relatively away from said first angular position against the bias of said spring means, pressure of said braking means against said spindle means decreases, allowing said spindle means to turn more freely, said braking means including a brake arm, rotatably mounted in the vicinity of said spindle means, and operative to engage said reel arm assembly, said braking means further including a second spring means, and a spring lever mounted on said brake arm, said second spring means biasing said brake arm such that said spring lever engages said spindle means, the rotation of said reel arm forcing said brake arm to rotate against the bias of said second spring means, thereby decreasing the pressure of said spring lever spindle means.
 2. An apparatus according to claim 1 wherein said roller guide is a cylindrical section, rotatably secured to said other end of said elongated reel arm assembly.
 3. An apparatus according to claim 2 wherein said reel arm assembly includes a plate member located at said one end of said reel arm assembly and rotating therewith, said first spring member being secured to said plate member, said plate member further mating with said brake arm, and being shaped such that a rotation of said reel arm assembly under stock pressure forces said brake arM to rotate in response thereto through the rotation of said plate member.
 4. An apparatus according to claim 3 wherein said plate member is shaped in the vicinity of its mating with said brake arm such that when said reel arm assembly is at said rest position pressure exerted on said spindle means by said spring lever is at a maximum, and when said reel arm assembly is gradually rotated against the action of said first spring member, the accompanying rotation of said plate member gradually forces said brake arm against the action of said second spring member, gradually reducing the pressure exerted on said spindle means by said spring lever.
 5. A tensioning apparatus, useful in a machine which includes a tape supply means, wherein the tape supply means includes a reel for receiving tape or the like, the machine being operative to exert a force on the tape, tending to cause the reel to rotate and the tape to unwind therefrom, the tensioning apparatus comprising: tape guide means engaging the tape as it is unwound from the reel, said tape guide means mounted to rotate about a first axis and yieldably biased into a first angular position about said first axis, said tape guide means being rotated against the bias thereon when the force is exerted on the tape by the machine; braking means yieldably biased into a stopped position engaging said tape supply means in a manner substantially preventing rotation of the reel; and, cam means rotatable with said tape guide means and engageable with said braking means and operative upon rotation of said tape guide means relatively away from said frist angular position to displace said braking means against the bias thereon relatively away from the stopped position, permitting rotation of said reel.
 6. An apparatus of claim 5, wherein said braking means is rotatable about a second axis spaced apart from said first axis.
 7. An apparatus of claim 5, wherein said cam means is engageable with said braking means substantially upon initial rotation of said type guide means, said cam means being so configured as to substantially uniformly increase the displacement of said braking means relatively away from its stopped position as said cam means is rotated, thereby gradually increasing the relative freedom of rotation of said reel.
 8. An apparatus of claim 5, wherein said braking means further includes means connected thereto and engaging said tape supply means in frictional engagement, the engagement of said resilient means and said tape supply means preventing rotation of the reel when said braking means is in said stopped position, the pressure of said resilient means against said tape supply means gradually decreasing as said tape guide means is rotated about said first axis under the external force, thereby permitting increasing freedom of rotation of said reel. 